I. Field of the Invention
This invention relates generally to apparatus for feeding sheet-like articles, one at a time, from the bottom of a stack of such articles.
II. Discussion of the Prior Art
Friction sheet feeders are known in the art and are commonly used in printers, plain paper copiers and the like to feed individual sheets, one at a time, from a stack of such sheets into the printer or copy machine. Friction feeders have also been used in mass mailing applications for assembling and collating packages of sheet materials between flights of a conveyor leading to a high speed wrapper.
It is important in such applications that the friction feeder deliver products one at a time in synchronized relation to the operation of associated equipment accurately, reliably and repeatably. For example, in the mass mailing application, a plurality of friction feeders are arranged along a length of a transversely extending conveyor and each such friction feeder must deliver only one article at the time from its stack onto the conveyor as each defined flight thereof passes the discharge end of the friction feeder. The friction feeder must therefore operate reliably, at high speeds, over prolonged periods and with a minimum operator intervention for clearing jams or multiple feeds.
Most prior art friction feeders include rollers or endless belts for supporting a stack of sheet articles thereon where the sheet articles are generally contained in a hopper mechanism. Associated with the endless belt or drive rollers is a gate member which is closely spaced relative to the endless belt such that the bottommost sheet in the stack will adhere to the endless belt and be carried through a gap while the penultimate sheet article and those above it in the stack are blocked from exiting until the bottommost sheet has cleared the nip. It is the function of the prior art gate member to allow low frictional resistance to the bottommost sheet being fed while at the same time providing a high frictional resistance at the gap through which the lowermost sheet passes to those sheets above it. A variety of such gate elements are disclosed in the prior art. For example, the Green U.S. Pat. No. 4,991,831 discloses a stationary cylindrical roll 51 disposed slightly above a friction feed belt and affording a higher frictional resistance to the penultimate sheet by providing a greater coefficient of friction at the nip than along a remaining surface thereof that normally abuts the leading edges of sheet articles in the stack. The Milo et al. U.S. Pat. No. 5,501,282 likewise utilizes a stationary gate member juxtaposed to the device's feed belt and which provides increased frictional resistance at the nip than along the remaining surface thereof by having an increased normal force at the nip than along the remaining portion of the gate member abutting the leading edges of the sheets in the stack. U.S. Pat. No. 4,651,983 to Long utilizes a friction wheel that is made to rotate in the same direction as the product movement, but at a slower speed to separate the articles in a stack of sheet articles in an attempt to allow only the bottommost sheet to pass through a gap between the drive and the gate member.
Other friction feeder manufacturers have utilized a stripper wheel that rotates in a direction which is opposite to the direction of flow of the sheet articles through the feeder in an attempt to separate the articles leaving the stack. In one such machine, however, the stripper wheel is only driven for about 50 percent of the feed cycle. That is to say, the stripper wheel was not designed to operate in a continuous motion, but only rotated 180.degree. for every complete rotation of the friction feeders belt drive shaft. The period of no motion of the stripper wheel has been found to result in frequent episodes of multiple product feeds for various sheet articles of differing texture and thickness as well as for certain feeding speeds.
The aforementioned machines suffer from a common problem. They do not provide an even and continuous pressure on the bottommost sheet article as it is being fed, resulting in its becoming skewed and leading to a jam condition at the discharge end of the feeder. Users frequently attempt to compensate for uneven pressure conditions by misadjusting (over tightening) the gate or stripper wheel pressure. This often leads to scuff marks and other damage to the sheet articles.